The invention relates to an improvement of a clutch device disposed between a gear of a member to be transmitted (hereinafter referred to as xe2x80x9ctransmitted memberxe2x80x9d) and a gear of a driving motor to transmit a driving force. The clutch device transmits the driving force to a member such as a sheet feeding roller in a copying machine, facsimile, printer and the like only when it is necessary.
As a clutch device used for transmitting the driving force to a sheet feeding roller in a copying machine and the like, there has been known a clutch device disclosed in Japanese Patent Publication (TOKKAI) No. 06-66328.
The clutch device includes a clutch hub as an input side, a driven pulley as an output side, a coil spring and a ratchet member. The coil spring is disposed for fastening a part of the clutch hub and a part of the driven pulley. One end of the coil spring is fixed to the driven pulley and the other end thereof is fixed to the ratchet member.
In a state that the ratchet member is free to rotate, the driven pulley rotates along with the clutch hub through fastening of the coil spring. Thus, the driving force is transmitted from the input side to the output side.
On the other hand, in a state that the ratchet member is locked, the coil spring expands. As a result, the clutch hub becomes idle and the driven pulley does not rotate.
In other words, according to the clutch device as described above, the driving force of the input side is transmitted to the output side only when it is necessary. In the case of the sheet feeding roller, for example, only when it is necessary to feed a sheet, the sheet feeding roller rotates.
However, in the conventional clutch device, the driving force is transmitted through the tightening force of the coil spring, i.e. frictional force. Therefore, it is difficult to transmit the driving force without loss. In other words, slipping occurs between the coil spring and a part of the clutch hub and a part of the driven pulley tightened by the coil spring when the driving force is transmitted, thereby causing loss of the driving force. To minimize the slippage as described above, it is necessary to use extra labor to assemble the device. Also, as a running torque on the input side becomes large, the slippage easily occurs. Therefore, the conventional clutch device is not suitable for transmitting the large torque.
When the driving force is not transmitted, the clutch hub is idle in a state that a part of the clutch hub is positioned inside the coil spring. Thus, a certain amount of a frictional force is produced between the coil spring and the clutch hub even when the driving force is not transmitted. The frictional force as described above provides an unnecessary load to the driving motor that always drives the clutch hub.
In a copying machine, it is required to reduce the electric power consumption as little as possible. Accordingly, there is a trend of using a single driving motor for driving components in the copying machine to reduce the unnecessary load to the driving motor as little as possible.
In view of the above defects, an object of the present invention is to provide a clutch device for transmitting the driving force to a transmitted member, such as a sheet feeding roller in a copying machine, facsimile, printer and the like, wherein when the driving force is transmitted, the driving force from an input side is transmitted to an output side without loss. Further, when the driving force is not transmitted, an input side rotor of the clutch device rotates idly while causing friction as less as possible.
Further objects and advantages of the invention will be apparent from the following description of the invention.
In order to attain the above objects, according to the first aspect of the invention, a driving force transmitting clutch device transmits a driving force to a transmitted member such as a sheet feeding roller in a copying machine, facsimile and printer. The clutch device includes a main shaft; an input side rotor rotatable around the main shaft; an output side rotor rotatable around the main shaft for transmitting the driving force to a member to be transmitted such as a sheet feeding roller; an inner sleeve member disposed between an input end of the input side rotor and an output end of the output side rotor for engaging the output side rotor in a state that the inner sleeve member moves only in an axial direction of the main shaft; an outer sleeve member disposed between the input end of the input side rotor and the output end of the output side rotor in a state that the inner sleeve member is received therein; a braking device for braking the outer sleeve member; a coil spring having one end fixed to the inner sleeve member and the other end fixed to the outer sleeve member for urging the inner sleeve member toward the input end of the input side rotor.
The inner sleeve member and the input side rotor are provided with main connecting portions so that the inner sleeve member engages the input side rotor through an urging force of the coil spring. The inner sleeve member disengages from the input side rotor when the inner sleeve member moves in a direction against the urging force. Further, the inner sleeve member and the outer sleeve member are provided with sub-connecting portions so that the outer sleeve member rotates when the inner sleeve member engages the input side rotor through the main connecting portions.
At least one of the sub-connecting portions of the inner sleeve member and the outer sleeve member is provided with a cam surface so that the inner sleeve member moves in a direction against the urging force when the braking device stops the outer sleeve member while the coil spring contracts a diameter thereof and is compressed or expanded in an axial direction.
An abutting surface facing the input end of the input side rotor is formed on the sub-connecting portion of the inner sleeve member. Also, an abutting surface facing the output end of the output side rotor is formed on the sub-connecting portion of the outer sleeve member. When the inner sleeve member is completely moved against the urging force, the abutting surfaces abut against each other through inertia of the inner sleeve member.
With the above structure, when the braking device does not stop the outer sleeve member from rotating, the clutch device is in an IN-state (driving force transmitting state).
More specifically, the main connecting portion of the inner sleeve member engages the main connecting portion of the input side rotor through the urging force of the coil spring. The inner sleeve member is assembled with the output side rotor to be movable only in an axial direction of the main shaft. Accordingly, the driving force on the input side rotor is transmitted to the output side rotor through the inner sleeve member to thereby rotate the output side rotor.
In the IN-state, the outer sleeve member also rotates around the main shaft along with the inner sleeve member through the sub-connecting portions of the inner sleeve member and the sub-connecting portion of the outer sleeve member.
When the braking device stops the outer sleeve member from rotating, the clutch device is in an OFF-state (the driving force is not transmitted).
More specifically, when the braking device stops the rotation of the outer sleeve member in the IN-state, the inner sleeve member is moved in a direction against the urging force, i.e. direction for releasing the engagement between the main connecting portion of the inner sleeve member and the main connecting portion of the input side rotor by the cam surfaces provided to both or one of the sub-connecting portions of the inner sleeve member and the sub-connecting portion of the outer sleeve member. When the engagement is released, the rotating force of the input side rotor is not transmitted to the output side rotor.
The inner sleeve member thus moved in the direction for releasing the engagement is slightly rotated further by the inertia. The abutting surface of the sub-connecting portion thereof is pressed against the abutting surface of the sub-connecting portion of the outer sleeve member. Thus, the main connecting portion of the inner sleeve member is not returned to a position to engage the main connecting portion of the input side rotor until the outer sleeve member is released. Therefore, in the OFF-state, the input side rotor rotates idly around the main shaft without load.
In a case that the coil spring is formed of a compression coil spring, the coil spring is compressed at the OFF-state. On the other hand, in a case that the coil spring is formed of a tension coil spring, the coil spring is elongated at the OFF-state.
When the outer sleeve member is released from the OFF-state, the clutch device returns to the IN-state.
More specifically, when the braking device releases the outer sleeve member from the OFF-state, the outer sleeve member is slightly rotated in the same direction as that in the IN-state by the restoring force of the coil spring with a contracted diameter in the OFF-state. The abutting surface of the sub-connecting portion of the inner sleeve member moves away from the abutting surface of the sub-connecting portion of the outer sleeve member. When both abutting surfaces do not contact with each other, the inner sleeve member is moved by the restoring force of the coil spring toward the input end of the input side rotor. Accordingly, the main connecting portion of the inner sleeve member engages the main connecting portion of the input side rotor again.
Thus, the output side rotor is again rotated by the rotation of the input side rotor through the inner sleeve member.
More specifically, according to the clutch device as described above, when the driving force does not need to be applied to the transmitted member, the input side rotor rotates without load, so that the clutch device does not apply the load to the driving motor for driving the input side rotor in the OFF-state. Also, in the OFF-state, it is possible to completely shut off the power to the output side rotor.
When the driving force is transmitted to the transmitted member, the rotating force is transmitted to the output side rotor without loss of the power through the engagement between the main connecting portion of the inner sleeve member and the main connecting portion of the input side rotor.
According to the second aspect of the invention, the driving force transmitting clutch device for the sheet feeding roller in the copying machine, facsimile, printer as described in the first aspect of the invention is provided with the braking device. The braking device includes a braking member and a connecting member. The braking member is provided with an engaging claw portion for engaging an outer periphery of the outer sleeve member, and a supporting point of a supporting member. The braking member also has a connecting portion of an urging device for positioning the braking member around the supporting point at a position where the engaging claw portion is always pressed against the outer periphery of the outer sleeve member.
The connecting member is attached to the braking member between the supporting point and the engaging claw portion for connecting the braking member and the supporting member in an elongated state. The connecting member is formed of shape memory metal alloy so that the connecting member returns to an original state before the connecting member is elongated when an electric current is conducted.
With the structure as described above, when the electric current is applied to the connecting member upon an input of a driving signal from the transmitted member, the connecting member is restored to the state before elongated to retreat the engaging claw portion of the braking member. Thus, the engagement between the outer sleeve member and the engaging claw portion is released, so that the outer sleeve member can rotate. In other words, it is possible to switch from the OFF-state to the IN-state.
When the driving force does not need to be transmitted to the transmitted member, the connecting member is elongated again upon turning off the electric current to the connecting member. The braking member is moved to a position where the engaging claw portion engages the outer periphery of the outer sleeve member by the urging force of the urging device to stop the rotation of the outer sleeve member again. In other words, it is possible to switch from the IN-state to the OFF-state.
With the braking member as described above, the braking device and the clutch device can be made compact and light as much as possible. It is also possible to reduce the electric power consumption of a copying machine and the like using the clutch device.